The app I wish I had in a college setting was a simple way of letting people know that I'm open to doing certain things at a certain time.
The best example i'm thinking about is like a pre-checkin feature for something like foursquare so friends can see I'm open to going to a bar/movie/dinner etc & they know it's worthwhile to call me, instead of having to do a bunch of back & forth messages to see who is up for any given thing at a time. Maybe this is because so many of my friends want to know "who else is interested" before they even express interest.